The Heteropoda belong to the “pelagic fauna” occurring near the surface in the Mediterranean and great oceans in company with the Pteropoda, the Siphonophorous Hydrozoa, Salpae, Leptocephali, and other specially-modified transparent swimming representatives of various groups of the animal kingdom. In development they pass through the typical trochosphere and veliger stages provided with boat-like shell.
Sub-order 1.—Taenioglossa. Radula with a median tooth and three teeth on each side of it. Formula 3 : 1 : 3.
Tribe 1.—Platypoda. Normal Taenioglossa of creeping habit. The foot is flattened ventrally, at all events in its anterior part (Strombidae). Otocysts situated close to the pedal nerve-centres. Accessory organs are rarely found on the genital ducts, but occur in Paludina, Cyclostoma, Naticidae, Calyptraeidae, &c. Mandibles usually present. This is the largest group of Mollusca, including nearly sixty families, some of which are insufficiently known from the anatomical point of view.
Fam. 1.—Paludinidae. Pedal centres in the form of ganglionated cords; kidney provided with a ureter; viviparous; fluviatile. Paludina. Neothauma, from Lake Tanganyika. Tylopoma, extinct, Tertiary.
 | |
| Fig. 29.—Pterotrachea mutica seen from the right side.(After Keferstein.) | |
a, Pouch for reception of the snout when retracted. c, Pericardium. ph, Pharynx. oc, Cephalic eye. g, Cerebral ganglion. g’, Pleuro-pedal ganglion. pr, Foot (mesopodium). | v, Stomach. i, Intestine. n, So-called nucleus. br, Branchial plume (ctenidium). w, Osphradium. mt, Foot (metapodium). z, Caudal appendage. |
Fam. 2.—Cyclophoridae. No ctenidium, pallial cavity transformed into a lung; aperture of shell circular; terrestrial. Pomatias, shell turriculated. Diplommatina. Hybocystis. Cyclophorus, shell umbilicated, with a short spire and horny operculum. Cyclosurus, shell uncoiled. Dermatocera, foot with a horn-shaped protuberance at its posterior end. Spiraculum.
Fam. 3.—Ampullariidae. To the left of the ctenidium a pulmonary sac, separated from it by an incomplete septum, amphibious. Ampullaria, shell dextral, coiled. Lanistes, shell sinistral, spire short or obsolete. Meladomus.
Fam. 4.—Littorinidae. Oesophageal pouches present; pedal nerve-centres concentrated; a pedal penis near the right tentacle. Littorina, shell not umbilicated, littoral habit. Lacuna, foot with two posterior appendages, marine, entirely aquatic. Cremnoconchus, entirely aerial, Indian. Risella. Tectarius.
Fam. 5.—Fossaridae. Head with two lobes in some Rhipidoglossa. Fossaria.
Fam. 6.—Purpurinidae, extinct.